The conventional control device for the AC rotating machine of this kind was disclosed in JP5-68398A (patent document 1). The control device for the AC rotating machine as disclosed in this patent document 1 comprises a current arithmetic circuit for computing a detected current value from each phase current flowing through the AC rotating machine, a correction frequency arithmetic circuit for computing a frequency correction value from the current set value and the detected current value in accordance with a predetermined arithmetic operation, a subtracter for subtracting the frequency correction value from a frequency command value, a voltage command arithmetic circuit for computing a voltage command value in accordance with the subtraction output of the subtracter, and voltage application means for applying a drive voltage to the AC rotating machine based on the voltage command value.
In the control device for the AC rotating machine as disclosed in the patent document 1, the detected current value is outputted by the current arithmetic circuit. If the detected current value exceeds a preset current set value, the correction frequency arithmetic circuit computes and outputs the frequency correction value by integrating at least a deviation between the detected current value and the current set value.
The frequency correction value is subtracted from a frequency command value inputted from the outside by the subtracter, and inputted as an inverter frequency into the voltage command circuit. The voltage command circuit computes a voltage command value in accordance with a preset functional relation, in which the voltage command value is outputted to the voltage application means. In the voltage application means, a drive voltage applied to the AC rotating machine is controlled to follow the voltage command value.
Herein, the correction frequency arithmetic circuit outputs the frequency correction value for correcting the frequency command value in accordance with a predetermined functional operation so that the detected current value may not exceed the current set value, irrespective of the power or regenerative state of the AC rotating machine. With such a configuration, the control device for the induction motor can protect an inverter circuit from over-current by conducting the current limiting operation which is stable not only during the normal operation but also during the hard acceleration or deceleration or the regeneration.    Patent document 1: JP5-68398A